Nuclear switch construction and method



June 7, 1960 J. H. COLEMAN 2,939,961

NUCLEAR SWITCH CONSTRUCTION AND METHOD Original Filed Aug. 15, 1951 3Sheets-Sheet 1 INVENTOR JOHN H. COLEMAN BY 14AM ATTO EY June 7, 1960 J.H. COLEMAN 2,939,961

NUCLEAR SWITCH CONSTRUCTION AND METHOD Original Filed Aug. 15, 1951 3Sheets-Sheet 2 4 m 94, W; 90, //z, A

INVENTOR JOHN HCOLEMAN ATTOR NEY June 7, 1960 J. H. COLEMAN 2,939,961

NUCLEAR SWITCH CONSTRUCTION AND METHOD Original Filed Aug. 15, 195] 3Sheets-Sheet 3 l I I INVENTOR JOHN H. COLEMAN ATTORNEY United StatesPatent NUCLEAR 'swrrcn CONSTRUCTION AND METHOD John H. Coleman, NewYork, N.Y'., assignor to Radiation Research Corporation, West PalmBeach,Fla., a corporation of Florida 7 Claims. (Cl. 250-106 This inventionpertains generally to electric switches, and more particularly tomethods and means for utilizing the kinetic energy of nuclear reactionsto provide for control of the electrical impedance between electrodes ina desired time sequence. This application is a division of my copendingapplication Serial No. 242,011, filed, on August 15, 1951, and which hasmatured as US. Patent No. 2,809,306 on October 8, 1957. H j Conventionalelectric switches utilize a moving conducr tor .to alter the, impedancebetween terminals or electrodes. For example, a'famili ar form ofmultipole switch em-- ploys a central rotary shaft carrying a conductivebrush which can make contact with a plurality of poles or termi-' nalsspaced in an arcuate array about the shaft. Such a switch has a limitedlife, due to abrasion between the moving contact brush and the fixedcontacts, and it is also sub-' ject to failure when dust particlesbecome lodged upon the contact surfaces, or when any cause interfereswith the making of contact in the desired sequence.

' Various other forms of switches have been proposed.Electronic'switches of the flip-flop (multivibrator or Eecles-Jordan)type eliminate the need for physical contacts, but they requireelaborateexternal power supplies'for the vacuum tubes employed. Capacitor typeswitches, in which the external circuit is completed through thecapacitance existing between a rotary member and one of a plurality offixed plates, have found limited application, for'example in antennaswitching. All such devices have objectionable features or limitations,which it is an object of thepresent invention to overcome.

In general, the present invention proposes the utilization of thekinetic energy of nuclear disintegration to provide a switch requiringrelatively few external power supplies. It is an important object of theinvention to provide a design for, and a method of operation of, aswitch which does not'require physical contacts'to be made andbroken tocontrol circuits.

- Another object of the invention is to provide a multipole switch inwhich desired circuits can be completed in a desired order, and in whichthe open-circuit impedance between terminals can be made very large;that is, one in which the open-circuit internal resistance is high, andthe leakage current very low. At the same time, the invention provides arelatively low closed-circuit impedance, so that 'the' change ofimpedance between the two conditions is large.

,Still another object of the invention is to provide a time-controlledmultipole switch employing nuclear ener-gy for the switching function,and free from the objections to the use of physical contacts for circuitcontrol.

- An additional object of the invention is to provide a switch in whichthe impedance between poles, when in closed circuit condition, can becontrolled in accordance with input-signals. A further-object of theinvention is to provide a switch of the above type which utilizes theinduced conductivity Patented June 7, 1960 I the building up of spacecharge in an insulator under potential stress, which can be extracted asuseful electric current upon reduction of the potential stress. Thisaspect of the invention is described in my copending application, SerialNo. 235,182, filed July 5, 1951, and entitled Method of and Means forCollecting Electrical Energy of Nuclear Reactions. l

The above and other objects and advantages of my invention will best beunderstood from the following detailed specification of certainpreferred embodiments thereof, given by way of example, reference beingmade to the appended drawings, in which:

Fig. "1 is a horizontal sectional view of one form of switch employingcylindrical symmetry, and having a solid dielectric and'a source of Betaradiation;

Fig. 2 is a fragmentary sectional view similar to Fig, 1

Fig. 5 "is a similar view, to a larger scale, of a planar form of theinvention utilizing features shown in Figs. 1 and 3; I

Fig. 6 is a similar view combining features shown" in Figs. 3 and 4;

- Fig. 7 is an illustration of a multiple collector elec trode structurethat of Fig. 1;

Fig. 8 is a view, partly in vertical section, of a structure havingcylindrical symmetry and utilizing a rotating dielectric body instead ofthe movable nuclear source of previous examples;

Fig.'9 is a view of a form similar to Fig. 8 but employ in anarrangement otherwise similar to ing both a movable radiation source andmovable elec trodes; and

Fig. 10 is a combination of several units of the Fig. 9' type, andproviding direct transformation of voltage to current in a highefficiency structure. Referring now to the drawings, and specifically toFig.

1 thereof, there is shown a switch comprising a.cylindrical shaft 10having a cavity extending inward from its peripheral surface andcontaining a quantity of a radioactive isotope 12 such as strontium 90.A thin metal sheet 14, such as stainless steel having a thickness of.002 inch, is pressed againstthe isotope 12 by a plug 16 threaded in thecavity, said plug having a central bore through which the radiation fromthe isotope 12 can pass. The shaft '10 can be rotated within asurrounding cylindrical shell 18 formed for example of .002 inchaluminum sheet and concentric with the axis of shaft 10. Outside thisaluminum cylinder isa cylinder 20 of a thin dielectric material suchas.002 inch polystyrene. Finally, collecting electrodes 22, which may besegments of conductivematerial, are disposed outside the dielectriccylinder.20.l These collecting electrodes may be assembled, as shown,-with intervening insulating spacers 24 so as to form completecylindrical collecting assembly.

Connections for the external circuits are illustrated in Fig. 1, thesecomprising a lead 26 from the rotary shaft 10 andalead 28 from aplurality of metallic shields 30, which may be blocks of metal securedto and in contact with the aluminum cylinder 18. The leads from theseeffect and the electrostatic hysteresis effect resulting from elementsmay be brought out at the end of the assembly, while leads 32 areprovided from the individual collecting electrodes 22. Leads 26 and 28are shown as connected together, so'as' to maintain the shields 30 atthe potential of shaft 10. i g

In operation, the shaft 10 is rotated, as by a motor or manually, sothat the radiation from source 12 is directed sequentially between theelectrode cylinder 18 and the respective collector electrodes 22. Theelectric current flowing bet-weenthese two electrodes can be the resultof three effects: (1) the primary Beta radiation, (2') the inducedconductivity in the dielectric body 210, and (.3 the induced spacecharge in such body. The first, or primary radiation effect, isproportional to the. quantity ofIisotope" or radioactive material 12.The second effect, induced conductivity, is a function of the quantityof the radiation and the type of dielectric employed. For example, thepolystyrene dielectric mentioned above, andpolyethylene, are reducedinvolume resistivity (which follows Ohms law under equilibrium conditions)from. around 10 down to- 101 ohm-centimeters, while amber is reducedless and arsenic sulphide is reduced more. The time required for theresistance to reach equilibrium'limits the: speed of motion of the shaftthatcan be employedwherr the induced conductivity effect is utilized;however, we have found the breakdown and recovery time of amber andarsenic sulfide to be in the milli-second range. The recovery time forpolystyrene is considerably longer being in. the range of hours.

The thirdeifect, which. I call electrostatic hysteresis, results in a.current flow between electrodes which is greater than the equilibriumvalue when the voltage is undergoing change. Thus, I have found thatwhen the inter-electrode potential difference has been reduced from someinitial value of equilibrium current flow down. to zero, currentcontinues to flow. The amountzoftcurrent that flows at zero potentialdifference is a function of the initial potential diiference and thequantity of'the radiation. Fig. 2 of the application referred toaboveillus. trates this effect for both positive to negative and negative topositive potential changes.

Since the insulating spacers 24 between the electrodes 22. would besubjected to radiation during the passage of the source 12 thereover,the relatively thick radiation shields 30 are provided to absorbsuchradiatiomsince these shields 30 are connected to cylinder 18, andthere by with one another, the lead 28 can be connected to lead 26 fromcylinder 10 and all of these adjusted to the same potential. Thus, nocurrent can flow due to the ions formed by collision of: the nuclearradiation with neutral. air molecules existingbetween shaft 10 andcylinden 18.

Rotation of shaft 10 thus cyclically lowers the electrical impedancebetween lead 26 and leads 32 from. the respective collector electrodes22, and in eifectprovides an: electricalcurrent-carrying connectionbetween these parts, permitting the control of external current-carryingapparatus. Vacuum tubes or sensitive relays may be con-' trolled in thismanner, and all of the switching functions of conventional mechanicalswitches can be achieved. Also,- since the switch in effect lowers theimpedance between the electrodes in sequence, suitableimpedancesensitive bridge circuits may also be controlled.

In Fig. 2, a modified form of the invention is shown, in which radiationfrom a source 34 is used toform a relatively low-resistance path betweenthe. shaft 10 and the surface of a cylindrical insulatorjbody 36.. Inthis 4 elements 38 can be connected as by leads 40 to an externalpotential such as that applied to shaft 10 via lead 26-, toguard againstleakage across the surfaces of the insulator segments 24. The leads 40in this figure are shown as brought out through the insulator segments24, but they may equally well be brought out the end of the cylindricalassembly. I

Fig. 3 of the drawings illustrates a modification simi- 7 lat? to'Fig. 1but employing a gaseous dielectric, and util case, the source 34produces Alpha radiation, and since 7 this radiation has lesspenetratingpower than the Beta radiation, thinner shields 38 may beemployed to protect the insulating segments 24. In this form of theinvention, there is no element corresponding to the electrode cylinder18*ofFig: ,1; as most of the ions formed by atmospheric collision willrecombine to neutral molecules in a region izing a fissiontype. ofradiation source. Again, numeral 10 designates the rotary shaft having.connecting lead 26, and surrounded by the thin. conductive cylinder 46.The outermost cylinder formed by the collector electrodesegments 22 isseparatedfrom electrode cylinder 46 by. a space 42 containing a suitablegas, and the collector electrode segments are separated fromone anotherby the insulator segments 44 which may also operate to support theconductive cylinder 46. Shields 48 and their leads 50 are alsoillustrated. In an actual embodiment of such a construction having aspaceof Ma between electrode 46 and electrodes 22,. and. usingair as adielectric, the volume resistivity changed from. greater than 10 ohmcentimeters to 10 ohm-centimeters with. an applied po; tential. up toabout 10 volts, with fast starting and recovery times. a 1

. Fig. 3 also illustrates a modified radiation source of the fissiontype; the cavity in. shaft 10 contains a neutron source 52 such. asastandard radium beryllium gun adjacent to a moderator 54, which may forexample be parainne wax, to slowthe emitted neutrons down to thermal.

velocities. The slow neutrons impinging upon the uranium 235 contained.in: the enriched foil 56- produce fission therein and consequentradiation of the desired type.

It is to be understood that any of thethree nuclear 112- actionsdescribed above can be employed, and even other types of reactions, inconnection with any of the various geometrical arrangements of theapparatus heretofore-or hereinafter. set forth, within theknown limitsof: penetrative power and other obvious controlling factors; well knownto those skilled in the nucleonics field.

Fig. 4 of the drawings illustrates a modified arrangement employing alinear arrangement'of the parts as obviously be employed wherecontinuous rotation in one direction is desired. Naturally, the partsbetweenshatt- 66 and the radiation source are in electrical circuit.Rotation of shaft 66 moves the piston or block 60 back and forth abovethe electrode assembly which may support the guides or tracks as byinsulator blocks 70. I i

The electrode assembly in this form of the invention provides completelyindependent sets of input and output terminals. To this end, individualrectangular metallic sheets 72 are separated 'by insulators 74 whose endfaces are guarded by strips-76 such as copper to prevent inducedconductivity between adjacent electrodes 72, and these" strips 76 areconnected to an external source of potential as by leads 78 to preventleakage currents across the insulator faces. As in previously describedembodiments, the leads 80 from electrodes 72 may be connected to'thesamepotential source as lead 68 in order to prevent flow of ionizationcurrents from the-source 58, 60 to the electrodes 72. Obviously,connections to the guides for the block 60 could be employed instead ofthe shaft connecting lead 68. The electrodes 82 are individuallyinsulated from. electrodes 72 by insulation 84 which may be-of the sameor similar materials as described inconnection. with. the previousembodiments.

Fig. illustrates a combined modification employing solid insulation 86for certain electrodes 88,- and gaseous insulation or dielectricmaterialindicated by 90 for others 92 of the electrodes. Various combinationsare thus possible to produce special results. Only certain of theelectrode connections are shown in- Fig. 5, it being understood that theother necessary connecting leads are provided in accordance with theprinciples set forth above.

A typical operational advantage illustrated in Fig. 5 is that the source96 may be made wide enough so that the relatively lower resistancegaseous dielectric 90 is irradiated while the trailing edge of theinsulation 86 is still receiving radiation. Electrode 92 is groundedthrough lead 94, and thus the common electrode 98 is grounded to providerapid recovery. As the source 96 passes on to the next section, thesolid insulation 86 will then be irradiated while the gaseous insulationis still undergoing irradiation, and the starting time is alsodecreased. The shields or absorbers 100 can be omitted when this type ofoperation is employed.

The embodiment of Fig. 6 is generally similar to that of Fig. 5, exceptthat individual electrodes 102 constitute the output electrodes (say),while the individual input electrodes 104 find a low-resistance path toground when the unshielded insulation 106 separating the latter isirradiated, the conductive path leading to the grounded electrodes 108when these unshielded insulators 106 are undergoing irradiation. Thisproduces the same effect as in Fig. 5 with respect to increased speed ofstarting and recovery.

Also shown in- Fig. 6 are temperature control elements 110; for example,electrical resistance heaters in heattransferring relation to electrodes104 and thereby to insulation 112 between the input and outputelectrodes. As is known, the conducting characteristics of insulatorscan be controlled by varying their temperature in this manner. It is tobe understood that these control elements 1-10 are merely exemplary;refrigeration can also be employed, and any such elements may beautomatically controlled by external means.

In Fig. 7, multiple collector electrodes 114, 11 6, 1-18 are shown,separated by solid insulating layers 120, 122. Connecting leads 126 forthe electrodes can be brought out through the insulating spacers 128 orotherwise. Parallel operation to lower the output resistance can beobtained in this way, by connecting the leads from alternate electrodelayers together as an input lead, and the remaining electrodes togetheras an output lead. Various other connection arrangements are possible.

Fig. 8 of the drawings shows a switch of somewhat differentconstruction, but employing the same principles as the forms describedabove. In this arrangement, a shaft 128 which is arranged to be rotatedas desired, carries a dielectric disc 130 a part of which is irradiatedby the radio-active source in a holder 132. The receiver electrode 134is connected to the source holder by a circuit including a variableresistor 136, the parts being made of common metals such as copper orsteel. The resistor controls the charging rate and the total chargebound upon the intervening area of the disc'130. As shaft 128 isrotated, the charged area of the disc ultimately passes betweenelectrodes 138 and 140, and is picked off by brushes represented asspringy contact fingers 142, 144. The current is led off to autilization circuit 146 by suitable connections. Rotation of the disc130 provides continuous operation with a desired time delay between thecontrolling impulse and the establishment of current in the outputcircuit.

An elaboration of the system just described is illustrated in Fig. 9, inwhich the source 146 is carried by an arm which can be moved radiallywith respect to the disc 130. The guide 148 for the source is insulatedas at 152 from the (fixed) collector 150, so that the external circuitmay include a bias battery or like source 156 and a source of controlpotential indicated schematically at 154.

6 A modulating signal can thus be used to vary the pattern of charge andvoltage carried by the disc. These"'pat-' terns can be internal spacecharge as described in com nection with Fig. l, or an overall potentialdrop between the two surfaces of the disc. If the charge is extracted inthe load at a different potential, the electrostatic hysteresis willcontribute an additional component of current which depends upon thetotal voltage to which the area of dielectric disc under considerationwas charged during its irradiation.

The receiver or charge pick-off assembly in Fig. 9 may again utilizebrushes 168 carried by holders 158, :160 secured to a yoke 162 movableas indicated by the arrowheads, the guides or tracks 164, 166 beinginsulated as at 170 from one another, with the external circuit 172connected between the holders as indicated. The radial motions of theradioactive source and of the pick-off unit maybe obtained in anydesired way. Clearly, the length of time between the establishment of acharge on a given elemental area of disc 130 and its reception at thepick-0t! device may be greatly extended as compared with the case ofimmovable source and pick-off; for example, by causing the charge tomove through several revolutions before the pick-off unit-is brought toa position where it receives such charge. Other types of operation canreadily be visualized.

Fig. 10 illustrates a further elaboration in that the shaft 174 carriesa plurality of spaced dielectric discs 176, the source 178 projectingradiation through all of these discs onto the collector 180. At anotherradial position, a

plurality of charge pick-off devices 182, again shown as resilientbrushes or fingers contacting the opposite surfaces of the disc, areprovided, and alternate pick-off leads are connected to the respectivesides of the utilization circuit 186, here shown as a load resistor. Thepick-off units may be supported as by having their support wiresembedded in the block of insulating material 184. When the discs arerotated, the induced voltages are taken oif in parallel, so that avoltage step-down,- and corresponding current step-up, is achieved. Inthe embodiment shown, this transformation ratio will be six to one. Itwill be understood that an input modulation signal can be applied to allof the discs in series at the irradiation point, or to individual discs,by employing means such as those shown in Fig. 9.

While the invention has been disclosed herein in certain selected andpreferred embodiments for purposes of illustration, it is to beunderstood that various other applications of the principles disclosedcan be made, and that modifications in structural details andarrangements can readily be effected by those skilled in this artwithout departing from the spirit of the invention as defined in thefollowing claims.

I claim:

1. In an electric switch having a contactor carrying a source ofionizing radiation and at least two contact segments disposed forconnection with said contactor by means of said ionizing radiation, anionizable dielectric for maintaining said contact elements electricallyinsulated from one another and a radiation shield interposed betweensaid dielectric and said source of ionizing radiation.

2. The switch of claim 1 in which said radiation shield is electricallyconnected to said contactor.

3. The switch of claim 1 in which said radiation shield is provided witha connecting lead for connection to a separate source of electricalenergy.

4. The switch of claim 1 in which said ionizable dielectric includes abody of solid dielectric material.

5. An electric switch of the type wherein connection between a conductorcarrying a source of ionizing radiation and at least one of a pluralityof contact segments is made by radiation induced ionization of anionizablc medium wherein said segment is spaced from adjacent conductiveelements by means of a body of solid di- 2,939,96 1- r 7 8 electric andarradiation shield is interposed between said References Cited in thefiie of this patent hady:and'said.ionizing radiation. UNITED STAT 1 TE Tr 6'. The switchhof claim 5 wherein said ionizable me- ES A N Sdiumi-comprisesiasolid dielectric. 3 393 W g 1944 7Y.1..'Fhe switch-ofclaim 5' wherein said ionizable me- 5 61 I Rqlsenblum T 1946' diamcompriseswa gas 7 2,683,813 Friedman Jul'y'13, 1954 2,692,951 Voelkel-Q. Oct. 26, 1954

